The present invention relates to metal plating and more particularly to substances used to increase adhesion during the metal plating process.
Many products are coated or plated with metal. Chrome, gold, silver and many other metal or metallic substances are used as coatings. The products being coated or plated are quite varied, including mirrors, automobile parts, light bulbs, and toys as a few common examples. Such products are coated for aesthetics (e.g. jewelry), reflectivity (e.g. mirrors), rust-proofing (e.g. some automobile parts) and a wide variety of other reasons. A common feature with all products, types of coating and purposes of the coatings is a strong desire for the metal plating to remain in place. Chipping and flaking are highly undesirable occurrences. Chipping or flaking of the metal or metallic coating is often the basis for disposal of the entire product.
Metallic coatings are applied to a variety of materials, including polymers, elastomers and metals. Of particular difficulty is causing a metal coating to remain adhered to elastomers and polymers. Metal plating has been performed using extreme vacuums to increase adhesion to some materials. Base coats, usually a lacquer or varnish, are used to increase adhesion between the substrate and the aluminum (or other metal) condensate. These base coats often do not stick to plastics or elastomers. The base coat will often crack when the elastomer is bent or otherwise deformed. These difficulties with the base coat lead to chipping or flaking problems with the metal coating. What is needed is an improved base coat or method of metal plating polymers and elastomers.
The present invention includes an adhesion promoter that is flexible and adheres to many elastomers and/or plastics. The inventive adhesion promoter provides a strong bond between the metal coating and the substrate and flexibility that avoids or diminishes the cracking and flaking common with products and methods of the past. Elastomers are often porous, providing poor surfaces for adhesion of the metal plate. The present invention creates a relatively non-porous skin at the surface of the elastomer, increasing the ability of the metal to adhere thereto.
The adhesion promoter is flexible and adheres to many elastomers and/or plastics. The promoter is preferably a resin-rich two-part epoxy such as xe2x80x9c3M Scotchweld 2216 Translucent Epoxy Adhesivexe2x80x9d, made by 3M Industrial Specialty Division, St. Paul, Minn. 55144, which can be dissolved in several solvents. The promoter, in its pre-cured state, is sprayed onto a substrate surface to form a thin relatively uniform film, which is then partially cured. A metal, such as Al, can then be vapor deposited after which the promoter, epoxy film, is allowed to fully cure, forming a bond not only with the substrate, but also with the metal coating.